Minor changes

- Implement freeing ircd struct
- Format callbacks struct more nicely
- Use a const message when handling datagrams
Allow specifying prefix when sending IRC message
Generalize broadcast event method
Handle nicks and messages. Don't connect to self.

Discover local cjdns address
Handle client quitting. Handle self-connections

Improve handling of self-connections by allowing them to happen, but just
not servicing them
Implement PART
Let ircd know its hostname
Improve handling of nicks and actions.

Ignore username.